Heavy rain and strong winds hit northern California overnight, leaving thousands without electricity, as a major winter storm that moved across the Pacific Ocean was set to hit the western U.S. state on Thursday. The National Weather Service (NWS) said more than 11 centimeters of rain has been reported in Sonoma County, north of San Francisco, and flood warnings were in effect early Thursday for points along the Russian and Navarro Rivers in Mendocino County and the Eel River in Humboldt County. Some tree damage and road flooding was reported in the region. Wind gusts peaking at 80 kilometers per hour (kph) were recorded on the Sonoma County coast, the NWS said. Authorities issued flash-flood and high surf and wind warnings ahead of the storm and said they were concerned that predicted heavy rainfall could lead to mudslides in wildfire-scarred foothills across the state. Early Thursday, power had been restored to 58 percent of the 30,000 customers that had lost electricity due to the storm, said Pacific Gas and Electric. Cities south of San Francisco were hardest hit, the utility said. Several area school districts, including San Francisco, Oakland, and Berkeley, canceled Thursday classes due to the winter storm. Authorities also issued advisories for residents to say away from jetties, piers, and rocks along the state's coastline to avoid getting washed into the ocean. Forecasters say the rain is expected to move across San Francisco Bay through midday and south to the Monterey Bay region. Southern California will start feeling the storm's effects by late Thursday. California is in the grip of a record-breaking multi-year drought that has forced officials to sharply reduce water supplies to farms and prompted drastic conservation measures.